The present invention relates to pyridazine derivatives, a method for its manufacture, compositions thereof including ultraviolet absorbents and photostabilizers, ultraviolet-ray-absorptive compositions and external preparations for skin.
Ultraviolet rays of wavelength 290 nm or less in sunlight are absorbed by the ozone layer. Accordingly, these do not reach the surface of the earth. However, as the ultraviolet rays of 290 to 400 nm reach the surface of the earth, these ultraviolet rays have various effects. In skin chemistry, the ultraviolet rays of the wavelength of 290 nm to 320 nm cause the formation of erythema and blistering. It is known that these ultraviolet rays cause acceleration of melanism and chromatosis. The long wavelength ultraviolet rays of 320 to 400 nm causes the melanism of skin immediately after irradiation. Also, since the energy reaches to an corium of skin, these ultraviolet rays influence the elastica in the walls of blood vessels and connective tissue. These ultraviolet rays of middle wavelength to long wavelength accelerate the aging of skin. Also, it is thought that these ultraviolet rays are a cause of the formation of stains, freckles, wrinkles and the like.
To protect the skin from such ultraviolet rays, ultraviolet absorbents have been used. These ultraviolet absorbents include, for example, benzotriazole derivatives, benzophenone derivatives, salicylic acid derivatives, p-aminobenzoic acid derivatives, cinnamic acid derivatives, and urocanic acid derivatives.
These ultraviolet absorbents are used in photostabilizers of colorant, perfume, drug, etc., in medical supplies and cosmetics.
Also, ultraviolet absorbents are used in fields other than medical supplies and cosmetics. For example, they are added to the various materials of coating, dye, pigment, resin, synthetic rubber, latex, film and fiber. As these are given absorbing ability for ultraviolet rays, a product, or paints or films coating a product can be protected from the ultraviolet rays. The ultraviolet absorbent is used to maintain quality by preventing degradation, degeneration and so on by the ultraviolet rays.
It is desirable that an ultraviolet absorbent is able to absorb the ultraviolet rays of all the wavelength range of 290 nm to 400 nm which reach the surface of the earth. Also, when an ultraviolet absorbent is included in an external preparation for skin, it is important that the ultraviolet absorbent is not decomposed by sunlight exposure. Also, it is important that the ultraviolet absorbent does not cause skin irritation.
However, conventional ultraviolet absorbents do not always satisfy these preferences. Conventional ultraviolet absorbents sometimes cause coloring and deposition due to ultraviolet rays shielding agents in inorganic powders commonly used in external preparations for skin. Also, a satisfactory photostabilizer compound has been needed.
Also, conventional ultraviolet rays absorbents in other fields sublimate and volatilize by heating during sintering of paints and in the forming of resin. In addition, these absorbents vaporize gradually and become less effective with the passing of time, even if it is not heated.
The present invention is achieved in view of the foregoing prior art. The object of the present invention is to provide an ultraviolet absorbent, a photostabilizer and a manufacturing method, which have an excellent absorbing ability in the wide ultraviolet rays wavelength range, that have high stability and safety. It is a another object of the present invention to provide an ultraviolet ray absorption composition including said ultraviolet absorbent. It is further object of the present invention to provide an external preparation for skin including said ultraviolet absorbent or said photostabilizer.
As a result of diligent study by the present inventors, it was found that a certain kind of pyridazine derivatives have the above-mentioned properties and are excellent ultraviolet absorbents and photostabilizers.
Namely, the present invention is pyridazine derivatives of general formula (1) and salts thereof. The compound of the present invention has excellent absorbing ability with respect to the wide ultraviolet ray wavelength range. As it is very stable and safe, it is an excellent ultraviolet absorbent and photostabilizer. 
A manufacturing method of the pyridazine derivatives comprises the process of reacting at least 10 wt % of 4,5-Dichloro-3-hydroxypyridazine or 4,5-Dibromo-3-hydroxypyridazine or combination thereof, with at least 20 vol % of morpholine in a reaction solution at 70xc2x0 C. or higher.
An ultraviolet absorbent of the present invention comprises said pyridazine derivatives and/or salts thereof as an active ingredient.
An ultraviolet ray absorption composition of the present invention includes said ultraviolet absorbents.
A photostabilizer of the present invention comprises said pyridazine derivatives and/or salts thereof, as an active ingredient. It is preferable that said photostabilizer includes a sequestering agent.
An external preparation for skin of the present invention comprises said ultraviolet absorbents. Also, it is preferable that the external preparation for skin of the present invention includes an inorganic powder.
Also, an external preparation for skin of the present invention comprises said photostabilizer. It is preferable that said external skin preparation includes a sequestering agent.
Also, in the external skin preparation of the present invention, it is preferable that said external preparation for skin includes 0.001 wt % to 20 wt % of said pyridazine derivatives or salts thereof.